1. Field of the Invention
The present invention relates to a propulsion system for a microsatellite, and, more particularly, to a micro-machined propulsion system formed with a small chamber closed by a diaphragm, which holds a small volume of a fluid or gas, such as inert gas. Heating of the fluid causes the fluid pressure to increase until the blow-out disk or diaphragm ruptures, which, in turn, causes the fluid to flow out of the chamber, acting as a propellant.
2. Description of the Prior Art
Microsatellites are satellites with massses ranging from 1 kilogram (kg) to about 10 kg. Nanosatellites are satellites with masses less than 1 kg. As used hereafter, all such satellites are identified as microsatellites. Microsatellites are used in a myrid of applications, including: sensor modules flying in formation with larger spacecraft radiation monitors; spectrometers; surface-charging monitors; CCD camera used in, imaging boom deployments and/or surface contamination monitors; constellations of satellites for communications systems; constellations of earth-observing satellites; distributed sensing the properties in the thermosphere; distributed weather satellites; surveillance satellites, for weapon system interceptors, and other applications.
Various microsatellites are known in the art. Examples of such microsatellites are disclosed in "Chemical and Electric Micropropulsion Concepts for Nanosatellites", by S. W. Janson, Copyright 1994, American Institute of Aeronaotics and Astronautics, Inc.; "Batch-Fabricated Microthrusters: Initial Results", by S. W. Janson and H. Helavajian, Copyright 1996, American Institute of Aeronaotics and Astronautics, Inc.
Conventional propulsion systems deliver too great a force and are too heavy for use with such microsatellites. Thus alternate propulsion systems are known to be used in such applications. For example, one known propulsion system for use in such an application, used primarily for orbit adjustment and satellite attitude control, provides a motive force to the satellite by introducing a propellant into a thrust chamber, reacting it and expelling it through the nozzle. Such a system consists of a minimum of 12 thrusters and a multitude of values, tanks, lines and sensors. Such a configuration is relatively complicated and relatively expensive to make.
A new class of microthrusters, as dicussed above, have been developed, that are adapted to be fabricated on a batch basis in a similar manner to microelectrons. Both chemical microthrusters and electric microthrusters are known. Chemical microthrusters include cold gas thrusters and hydrazine monopropellant thrusters. Cold gas thrusters include a converging/diverging nozzle that is used to expand the propellant, such as hydrogen, nitrogen or helium to develop an impulsive force. Unfortunately, the storage density of hydrogen at practical pressures and temperatures for use in a microsatellite is impractical.
Hydrazine monopropellant microthrusters are also known. Such hydrazine monopropellant thrusters are relatively complicated and include a large number of moving parts such as a nozzle, and a large number of moving parts such as a nozzle, and a microvalve array. Such monopropellant type microthrusters also require a microcontroller.
As mentioned above, electric microthrusters are also known. Such electric microthrusters include resisto-jets as well as electrostaticthrusters. As generally described in "Chemically and Electrically Micropropulsion Concepts for Satellites", supra, resisto-jets use electric heaters to expand the pressure of a propellant which, in turn, is expelled through an exhaust nozzle, creating a motive force. The problem with known resisto-jet type microthrusters is the volume of storage space required for the propellant. Electrostatic microthruster, on the other hand, require metal in a molten state.